Process and system for producing synthetic crude from coal



lPROCESS AND SYSTEM FOR PRODUCING SYNTHETIC CRUDE FROM COAL Filed March4. 1968 United States Patent O 3,503,867 PROCESS AND SYSTEM FORPRODUCING SYNTHETIC CRUDE FROM COAL Leslie L. Ludlam, Garden Grove,Milan Skripek, Anaheim, and Kenneth E. Whitehead, Fullerton, Calif.,assignors to Atlantic Richfield Company, Philadelphia, Pa., acorporation of Pennsylvania Filed Mar. 4, 1968, Ser. No. 710,036

Int. Cl. Cg 1 00 U.S. Cl. 208-10 8 Claims ABSTRACT OF THE DISCLOSURE Aprocess is disclosed for producing synthetic petroleum crude from coal,for use in a petroleum refining system, which includes low temperaturecarbonization of dried pulverized coal, hydrocracking of the combinationof middle oil, tar and naphtha, vacuum distillation and secondaryhydroheating of the low volatility components derived from thehydrocracking process and fractionation of the high volatilityhydrocarbons from the hydrocracking unit and the secondarilyhydrogenated low volatility components derived from the hydrocrackingprocess.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a process and apparatus for producing liquid hydrocarbonproducts from coal. More specifically, this process relates to methodsfor producv ing synthetic petroleum crude by carbonization of coal andhydrotreating of coal tar products.

Description of the prior art There has -been a continuing interest inutilizing coal as a source of liquid hydrocarbon products since theadvent of the internal combustion engine. Several processes have beendeveloped which have attained technical importance to countries havinglimited access to petroleum reservoirs. A number of processes weredeveloped in Germany to offset shortages in petroleum during World WarII.

Of recent years, there has been a revival of interest in severalprocesses for producing synthetic petroleum crude from coal, ResearchersDisclose Cost of H-Coal Gasoline, Oil and Gas Journal, May 16, 1966, p.155; Coal Knocks at Refinery Door, Chemical Week, Feb. 11, 1967. p.29-35. While numerous processes have been proposed for producing liquidhydrocarbon synthetic petroleum crude from coal and the technicalfeasibility of a substantial number of these processes has been proved,no commercially feasible process of this type has been put intooperation. Accordingly, it is an object of this invention to provide acommercially and a technically feasible process for producing syntheticpetroleum crude from coal.

Processes for producing synthetic crude from coal range from theso-called topping processes wherein only a very minor fraction of themore volatile products produced by mild destructive distillation of coalis converted to liquid hydrocarbons, the remainder of the coal ybeingburned in the normal manner to produce steam, and those wherein aneiiort is made to convert essentially all of the carbon content of coalto liquid hydrocarbons. Exemplary of the latter class of processes arethose described by Clark et al., Hydrogenation of Coal in a FluidizedBed, Industrial and Engineering Chemistry, May 1961, p. 861-865; andHellwig, et al., Make Liquid Fuels from Coal, Hydrocarbon Processing,vol. 45, p. 165-169, May 1966. In the former case, coal is carbonized inthe dry 3,503,867 Patented Mar. 31, 1970 ICC state, the liquids andvolatile components being carried out of a iluidized bed. In the lattercase, coal is suspended in a liquid phase, which may consist of tar,along with a catalyst.

A number of processes have also been proposed wherein coal is subjectedto a more severe carbonization or hydrogenation treatment to convert anintermediate fraction of the coal to liquid hydrocarbon material,leaving the more diicultly converted coal components for cornbustion inthe normal manner; i.e., in coke-fired furnaces.

There is reason to believe that the most economical and commerciallyfeasible process will be of this latter type wherein, by carefullybalancing the energy requirements for converting coal fractions toliquid hydrocarbon materials against the value of the hydrocarbonmaterials produced, the value of the synthetic crude, plus the value ofthe less valuable combustible solid coal products and the by-productswill substantially exceed the cost of treating the coal.

Since the most valuable of the products of the coal treatment process isthe synthetic petroleum crude it will'ibe understood that the commercialfeasibility of any such process is very largely dependent upon thequality, and hence the value, of the synthetic crude produced. Foroptimum value, the synthetic crude should be of such a quality that itcan be lprocessed in a conventional petroleum refinery, along withpetroleum crude, without substantial alteration of operating conditions.It has been suggested, however, that certain superior grades of fuel maybe produced from synthetic petroleum crude derived from low temperaturecarbonization of coal. Accordingly, it as an object of the presentinvention to provide a method for producing synthetic petroleum crudewhich is, in its renery characteristics, substantially identical withhigh quality petroleum crude.

A large number of coal carbonizing processes are known; see e.g., Farr,Coal Carbonization New Methods and Objectives, Coal Age, December 1966,pp. 88-96, and hydrocracking of liquid hydrocarbons, most particularlypetroleum crude, and hydrotreating of liquid hydrocarbon materials arewell known in the prior art. The present invention constitutes animproved combination of such known treating steps and includes novelcycle and recycle steps.

SUMMARY OF THE INVENTION Without limiting the scope or applicability ofthe invention, the present process may be described, in its principalsteps, as including the low temperature carbonization of coal forconverting the more valuable carbonaceous components to liquidhydrocarbon materials, feeding the liquid `hydrocarbon materials andnaphtha through a hydrocracking step, vacuum distilling the heaviercomponents from the hydrocracking step and recycling the solid and lowvolatility components to the carbonizer, secondarily hydrotreating thevolatile components from the vacuum distillation step and combining themore volatile components from the hydrocracking step and the secondarilyhydrotreated components for fractionation to produce a syntheticpetroleum crude for being handled according to conventional petroleumrefining techniques. It is, accordingly, a principal object of theinvention to provide an improved method for producing synthetic crude ofa qualityk comparable to petroleum crude by low temperaturecarbonization and hydrocracking of coal components.

A more specific object of the invention includes the addition of naphthacomponents for combination with tar and middle oil components in thehydrocracking step of a process of the type disclosed.

A further specic object of the process disclosed includes thecombination of phenols from the carbonizer in the secondaryhydrotreating step for increasing the synthetic crude yield.

An additional object of the invention is the provision of a system forcarrying out a process of the type described.

A further and more specific object of the invention iS the provision ofa novel combination carbonization and hydrogenation system forextracting liquid hydrocarbon fractions from coal.

Other objects will be apparent from the specification which follows andfrom the drawings to which reference is now made.

BRIEF DESCRIPTION OF THE DRAWING The figure is an overall schematicdiagram showing the system for carrying out the inventive process andillustrating the process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is made now to thefigure. The major components of the preferred system for carrying outthe inventive process comprise a low temperature carbonizer 10, ahydrocracking unit 20, a vacuum still 30, a hydrotreater unit 40, and afractionator 50. Auxiliary units which comprise important elements inthe system include a char pulverizer 6i), a phenol extractor 70, anammonia stripper 80, a naphtha recovery unit 90,*an acid gas removalunit 100, and a hydrogen generator 110.

The components of the system are, individually, known in the prior artand have been described. For example, the low temperature carbonizer maybe of the type constructed by Lurgi Gesellschaft, Frankfurt am Main anddescribed in the Lurgi Manual (1961). This process is also described byPeters, W. and Bertling, H., American Chemical Society Division of FuelChemistry Preprints, vol. 8, No. 3, pp. 77-88; (148th National AmericanChemical Society meeting, 1964). The carbonization unit consists ofthree main sections, carbonization, heat generation and volatilescollection, and utilizes hot char recycle to supply heat for thecarbonization. Dried coal is fed by a double screw mixer, where it ismixed with hot recycle char, into the carbonization chamber. As thesolids leave the mixer, they fall into the devolatilization vessel ofthe carbonizer at a temperature of from 800 to 1250 F., preferably about1100 F. The devolatilization vessel is substantially free of air. Hereslow devolatilization reactions are allowed to proceed, giving maximumyields of gas and liquids from the coal. This overall technique, whichis termed flash carbonization, provides the Very rapid solid-solid heattransfer which is essential for maximum devolatilization of coal. Thisprocess gives higher liquid yields than gas-solid heat transfer yields.Char from the carbonization zone ows by gravity through a gas seal atthe bottom of a lift pipe and the heat generation zone of the carbonizerand is conveyed upwardly by a high velocity mixture of flue gas and airwhere part of the char is consumed with the air to produce heat. Char at1250 F. is collected in a bunker and allowed to flow by gravity forrecycling into the inlet of the double screw mixer. Excess char isremoved.

It should here be pointed out that the type of carbonizing unit justdescribed has been used and found to be successful in the overallprocess; however, other carbonizers have been used as well with varyingdegrees of success and the description herein is simply exemplary of thepreferred embodiment of the invention and the process is not limited tothe use of the Lurgi-Ruhrgas (L-R) type carbonizer. The liquid output ofthe L-R carbonizer, as will be discussed in some detail hereinafter,comprises two streams, tar and middle oil, which are subsequentlycombined for treatment. Other carbonizers may produce only one outputstream of tar which will be referred to herein as light tar todistinguishthis product from the heavier tar output stream of the Lurgicarbonizer described in the 4 exemplary embodiment. Light tar obviouslycan be produced simply by premixing the middle oil and tar prior totreatment if desired.

The hydrocracking unit is specifically designed to handle extremelyheavy feed stocks. This unit may be of the type associated with theH-Oil process which has been described; e.g., Helwig, et al.,Hydrocarbon Processing, supra; Chervenak, M. C., et al., H-Oil ProcessTreats Wide Range of Oils, Petroleum Rener, vol. 39, No. l0, pp. 151-156(October 1960); Rapp, L. M., and Van Driesen, R. P., H-Oil Process GivesProduct Flexibility, Hydrocarbon Processing/Petroleum Refiner, vol. 44,No. l2, pp. 103-108 (December 1965); and Prescott, J. H., Novel RouteUpgrades the Bottom of the Crude Barrel, Chemical Engineering, vol. 72,No. 15, pp. 142-144 (July 18, 1966).

The aforementioned publications are incorporated by reference for thedetails of the process but the following brief description is given forcompleteness. The feed oWS upwardly through a reactor which contains asuspended catalyst to produce an ebullated catalyst bed. Isothermalconditions can be maintained in the bed even with highly exothermicreactions and the ebullated bed is capable of handling feed stocks whichcontain entrained solids or which tend to form coke readily.

The vacuum still 30, the secondary hydrotreater 40, and the fractionator50 are all conventional units of the type used in petroleum rening. Thechar pulverizer 60 may be o-f any conventional typefand the phenolextractor 70 may be a Phenosolvan unit in which phenol-rich water iscontacted contracurrently lwith isopropyl ether and the extract solventis distilled to produce a crude phenol product. Units of this type andother phenol extraction units are in operation commercially, and aredescribed in the Lurgi Manual, supra.

The amm-onia stripper is of conventional design and may be combined witha water treatment system, if desired.

The naphtha recovery unit is preferably of the type wherein the gasesand highly volatile components from the carbonizer 10, the hydrocrackingunit 20, the hydrotreater 40 and the fractionator 50 are combined andscrubbed with middle oil to remove the naphtha. The naphtha, carried bythe middle oil or light tar, is then recycled as will be described.

In the acid gas removal unit 100, all of the HZS and most of the CO2 areremoved by methanol extraction. The sulfur-containing gases are treatedin the conventional manner to recover the sulfur values therein.

Hydrogen is generated, in the hydrogen generator unit 110, by reactionof carbon monoxide and steam to form CO2 and H2 according to knownreactions. The gases are then catalytically reformed to convert thehydrocarbons and steam to CO, CO2 and H2. The CO in the gas reacts withresidual steam to complete the conversion to CO2 and H2. Units of thistype are also known commercially.

It will be apparent from the foregoing that most of the units of theinvention are, individually, known in the prior art and are in generalof the types commercially in use and which have been described in theliterature. It is the novel combination of such units which comprisesthe present invention.

Referring now to the ligure, the process of this invention will bedescribed.

Dried coal, which may include recycled hot char, passes from line 9through a vapor lock into the lo'w temperature carbonizer 10.Non-volatilized coal components pass by gravity through a pressure sealto exit line 11. The tar components of the volatilized coal productscomprise the heavier liquid fractions and entrained solid particulatematter and are transferred through line 12 to the hydrocracking unit 20.The middle oil fractions are also fed to the hydrocracking unit 20through line 13. It will, of course, be remembered that in the inventiveprocess using a different type of carbonizer only one liquid Stream,light tar, which may include entrained particles, will be produced or alight tar may be produced by c-ombining the tar and middle oil fractionsfrom the Lurgi carbonizer described in the example.

The more volatile components, including the highly volatile hydrocarbonsand xed gases produced or released by the low temperature carbonizationprocess exit through line 14. The aqueous components are condensed andare withdrawn from the carbonizer through line 15 carrying the watersoluble components, primarily phenols and arnmonia. Fractions of theflue gas from the carbonizer may be recycled through the coal dryer asshown at line 16 to conserve heat values.

The low vapor pressure liquids and entrained solids are removed from thehydrocracker 20 through line 21 to the 'vacuum still 30. The high vaporpressure hydrocarbons leave through line 22 to the fractionator as willbe described more specifically hereinafter. Gaseous components and thevery light hydrocarbons are carried through line 23 to the naphtharecovery system as will be described. Ammonia-rich waste water iscondensed and is withdrawn through line 24 to the ammonia recovery andwater treatment system.

The major portion of the synthetic crude hydrocarbon fractions exitthrough line 31 from the vacuum still 30 to the hydrotreater 40. Thestill bottoms, including the solid material, are recycled through line32 to the low temperature carbonizer 10.

T he upgraded synthetic crude is transferred from the hydrotreater 40through line 41 where it is combined with the high vapor pressurehydrocarbons exiting from the hydrocracking unit 20 through line 22 andfed to the fractionator 50 which separates the syncrude (syntheticpetroleum crude) which exits through line 51 and may be transported tothe renery, and the light hydrocarbons together with small quantities ofthe more highly volatile naphtha components which are returned throughline 52 to the systemi Returning again to the rst steps in the process,the char from the low temperature carbonizer is removed through line 11to the char pulverizer 60 and thence through a conveyor line indicatedat 61 for recycling or for combustion as conventional coke.

Phenols from the phenol extractor 70 are conveyed through line 71 to thehydrotreater 40 for being upgraded, along with the hydrocarboncomponents from the vacuum still 30, to form the synthetic crude. Theaqueous phase from the phenol extractor is combined with the aqueousphase from the hydrocracking unit 20 and from the secondary hydrotreater40 and flows through line 72 to the ammonia stripper 80. Ammonia isremoved through line 81 vto any desired type of ammonia recovery systemfor the production of fertilizer, industrial chemicals, etc. Waste waterfrom the system exits through line 82 to a water treatment plant and isdischarged.

The light hydrocarbons, naphtha and xed `gas streams are collected fromthe low temperature carbonizer 10 through line 14, the hydrocrackingunit 20 through line 23, the hydrotreater 40 through line 42 and thefractionator 50 through line 52 and enter the naphtha recovery unit 90.As previously described, the naphtha is removed by scrubbing with middleoil and recycled through line 91 where it is combined with middle oil orlight tar output of the low temperature carbonizer and fed to thehydrocracking unit 20. Recycling the naphtha in the manner describedprovides several importat advantages. The hydrocracking step .of theprocess may be more easily and eliciently conducted by recycling thenaphtha in the manne; described and the quality of the synthetic crudeis improved. It is entirely possible that the recycle step in theprocess described may make the difference between an economicallypractical system and a system which, while eing technically feasible, isnot economically attractive.

The light hydrocarbons and fixed gases llow from the naphtha recoveryunit through line 92 to the acid gas removal system. Thesulfur-containing components are carried through line 101 to the sulfurrecovery unit. The remaining gases, primarily carbon monoxide, hydrogen,and gaseous hydrocarbons, exit through line 102. Fuel gas for providingheat at the necessary points throughout the entire system and fordistribution to public utility gas companies is drawn olf through line103. Enough of the hydrogen-containing gas is drawn through line 104 tothe hydrogen generator to operate the hydrocracking unit 20 and thehydrotreater 40. As previously described, the hydrogen generatorconverts substantially all of the gas components to carbon dioxide andhydrogen with only traces of methane remaining. The carbon dioxide isdrawn olf at 111 for purication and sale as an industrial gas orsolidifcation and sale for refrigeration purposes. The hydrogen,containing the traces of methane, is drawn olf through line 112 anddistributed through lines 113 and 114 to the secondary hydrotreater 40and the hydrocracking unit 20.

By careful control of the operating conditions of the system, especiallythe low temperature carbonizer, the hydrocracking unit, the secondaryhydrotreater, the naphtha recycle system and the hydrogen generation andrecycle system, the process' may be balanced so that the maximumquantity and quality of synthetic petroleum crude is produced with aminimum consumption of heat. Optimum 'operating conditions are achievedwhen the value of the synthetic crude components extracted exceeds themarketable heat value of the char, giving consideration to the marketvalue of the byproducts. Deeper extraction of hydrocarbon values fromthe coal may result in a relative net loss.

Careful consideration of the economic factors which control the relativevalues of the products of the described process will suggest the verysignificant advantage the present process has over the processes of theprior art. If the heat value of char or coke and the value of syntheticcrude, as well as the values of the minor byproducts were fixed, asingle set of process conditions could be determined which would resultin maximum economic benefit to the operator and lower costs to thepublic. As is Well known, however, the market values for each of theproducts of the process described fluctuate according, e.g., to seasonaland industrial demands, the political forces in operation at a giventime and general economic conditions. It is, therefore, highly desirableto provide a system and a process which can be varied to produce maximumeconomic value as the values of the individual products of the processshift. In the present process, the only products which will have asubstantial effect upon the process variables are, of course, therelative values of char as a fuel and of the synthetic crude. Aspreviously pointed out, however, the value of the synthetic crude isvery highly dependent upon its quality.

Taking into consideration current economic and techni- 'cal conditionsthe following operating conditions are given as exemplary of a preferredembodiment of the invention, on a small pilot plant scale.

Coal from the Last Chance Creek outcrop of coal beds in southern Utah,known as Kaiparowits coal, was crushed and screened to pass through a 1Ainch mesh screen. This grade of coal contains about 6.4 percentmoisture, 40 percent volatile matter, 7.3 percent ash, and 46.3 percentxed carbon. Of course, other sub-bituminous coals, Such as those knownas .Black Mesa coals from northern Arizona, or any roughly equivalentgrade of coal may be used. The coal was dried to 3 weight percentmoisture by countercurrent contact with hot ue gases from thecarbonizer. These ue gases are byproducts of the char of combustion inthe heat generation portion of the carbonizer. Any type of dryer may beused but the dryers found effective in this embodiment were Verticalcolumns .for dilute phase contact between hot gases and the wet coal,electrostatic precipitators being used to remove solids from thewater-saturated waste gases.

The crushed, dried coal was fed to the double screw mixer of thecarbonizer where it was mixed with hot recycle char. Contact time in themixer is only a few seconds but a large percentage of thedevolatilization of the coal occurs during this interval. The coal-charmixture was conveyed into the carbonization vessel of the previouslydescribed carbonizer. The average temperature of the coal in thecarbonizer vessel was 1100 F.

The tar and middle oil components were fed into an H-Oil hydrocrackingunit of the type described. The tar and middle oil are pumped separatelyinto the unit and are preheated by exchange with the hot reactor liquidand fed into the reactor countercurrently with the recirculatinghydrogen stream. Light tar is similarly treated, except that only oneliquid feed is required.

The mixed phase high pressure product is allowed to separate afterleaving the catalyst bed. This physical separation may occur in theupper section of the reactor or in an external vapor-liquid separator.Subsequent cooling and flashing of both streams allows recovery of mostof the hydrogen from the products. Butanes and lighter are stripped fromthe stream and the low pressure liquid product is sent to the vacuumstill.

The vacuum still is operated at 900 F. and supplies a solids-free feedto the secondary hydrotreater 40. The vacuum bottoms, as previouslydescribed, are recycled to the carbonizer and coked.

The 900 F. end-point vacuum still overhead is preheated by exchange withthe reactor eiuent and fed to the secondary hydrotreater reactor.Hydrotreating, in an exemplary embodiment, may be done over CyanamidHDS-3A Ni-Mo catalyst at about 1750 p.s.i.g. hydrogen, 750 F., and aliquid hourly space velocity of about 1.0. The reactor efiiuent iscooled to about 100 F. and ashed to separate hydrogen-rich recycle gasesfrom the liquid products. Water settles by gravity from the oil productsand is sent to the waste water cleanup system.

Low-pressure flash vapors and the unstabilized hydrotreater oil productare combined and fed into the hydrotreater fractionator. Butanes andlighter hydrocarbons are stripped from the synthetic crude product inthis tower and sent to the gas cleanup facilities at the hydrogen plant.The high-pressure component from the fractionator is the synthetic crudeand is now ready for shipment to a renery. Desirably, but notnecessarily, the coal liquefcation plant may be located adjacent areinery so that the entire production and refining of syncrude may becarried out continuously. In the speciiic embodiment, however, thesyncrude was collected for further refining.

The gases and high 'vapor pressure hydrocarbons produced in the severalstages of the process are rst scrubbed with middle oil to remove thenaphtha. The naphtha contains large quantities of oleiins and dioleiinsand requires hydrogenation and, therefore, is absorbed in middle oilwhich also requires upgrading. This eliminates the need for adistillation column to regenerate a lean oil stream.

The high pressure gases from which the naphtha has been removed are fedto the acid gas removal unit, which may be a Rectisol extraction tower,described in the Lurgi Manual, where all of the HZS and most of the CO2are removed by extraction with methanol. This unit also includesequipment for solvent (methanol) regeneration.

The scrubbed gases from the Rectisol plant are then sent to the hydrogenplant as required to produce hydrogen for the process.

The other auxiliary units operate under conventional process conditionswhich have been described.

Complete data on the composition of the syncrude resulting from theabove process are not yet available; however, the product appears to becompatible with petroleum crude in all respects and may be processed ina conventional petroleum rening process. There is considerable evidencethat the relative energy content of the syncrude produced by thisprocess is substantially higher than the energy content of a comparablequantity of conventional petroleum crude. A There is considerableevidence to indicate that the vacuum distillation step is essential tothe operability of the process although this was not `denitelyestablished. The liquid tar products derived from the prior stages, ifhandled immediately without significant delay in transit or holdup time,could be processed with some difficulty. However, where there was anyappreciable holdup time between one stage and the following, there was atendency for the material to harden and become a thick black mass ofapparently polymeric material which could not be handled by anyconventional reiinery process. l

It was determined that the components which were causing the difficultyconstituted only a small fraction of the total composition of the liquidtar material. Initialy it was believed that a vacuum distillation stepmight result in substantially reduced yields but, surprisingly, this didnot result. Probably less than 15 percent of the total material wasobjectionable and caused the diicult handling problems. IUpon removal,by vacuum distillation, of this fraction and recycling it through theprevious steps, substantially total potential yield was obtained and theend product was easily handled according to conventional reiiningtechniques.

On this basis, the vacuum distillation stepappears necessary at leastfor application in a commercially successful processing operation.

-Review of pilot plant operations indicates that improved tar qualitymay result from the carbonization process utilized but optimum valueswere not determined. It is to be emphasized, however, that any type oflow temperature carbonization process may be utilized as an individualstep in the inventive process without departing from the scope andspirit of the invention which iS defined in the claims.

It will be understood, also, that the embodiment given is merelyexemplary of the invention and that the conditions given are notnecessarily limiting but rather indicate a workable operating condition.With these considerations in mind there are several areas in Iwhich itis known and/or expected that certain operating conditions may be variedto improve either the quality of the product or to improve the overallefficiency of the process. For example, While complete `data are notavailable to coniirm these iindings, there is good reason to believe,based on preliminary data, that as the fraction of the coal which isliqueiied to produce synthetic crude is increased the overall quality ofthe crude tends to go down. That is, the hydrogen content and the energycontent as well as the compatibility of the syncrude with petroleumcrude, are reduced. Thus, the severity of the coking operation is, froman economic standpoint, dependent in part on the quality of the syncrudewhich is desired. Similarly, the percent of the tar which is convertedin the H-Oil process may be varied by changing the operating conditionsin that process. Initial indications are that between 60 and 80 volumepercent of the tar is converted to raw syncrude but it is expected thathigher conversions can be obtained through optimization of the processvariables. The operating conditions in the secondary hydrotreater have,likewise, not been optimized and significant advances are to be expectedfrom further experimentation. Obviously, modifications can be expectedto result from operating experience based on known engineeringprinciples and Ifrom the process described herein.

lFrom the foregoing speciiication it will be apparent that a highlyuseful and commercially valuable process has been disclosed and thatwhile a particular embodiment of the invention has been disclosed indetail departures may be made from the exemplary embodiment withoutdeparting from the scope and the spirit of the invention as defined inthe following claims.

9 We claim: 1. The process for producing synthetic petroleum crude fromcoal which comprises the steps of:

carbonizing coal at a relatively low temperature to produce a stream ofhighly volatile uids including naphtha and at least one additionalstream of higher molecular weight normally liquid products;

hydrocracking the normally liquid products to produce a stream of highlyvolatile fluids including naphtha and a stream of normally liquidproducts;

vacuum distilling the normally liquid products to produce a stream ofsynthetic crude;

hydrotreating the synthetic crude from the distilling step to produce astream of improved synthetic crude and a stream of highly volatile uidproducts including naphtha;

lfractionating the improved synthetic crude to produce a stream ofsynthetic petroleum crude having refining properties substantiallyequivalent to lnatural petroleum crude;

combining the naphtha-containing streams;

stripping the naphtha from said combined streams; and

recycling at least a portion of the naphtha by combining said naphthawith the normally liquid products from the carbonizing step prior tohydrocracking said products.

2. The process of claim 1 wherein the carbonizing step produces anormally liquid tar stream and a middle oil stream, at least a portionof each of said streams being separately fed to the hydrocracking step.

3. The process of claim 2 wherein the recycled naphtha is mixed with themiddle oil prior to hydrocracking.

4. The process of claim 1 wherein the normally liquid feed from thecarbonizer to the hydrocracker is light tar and the naphtha is premixedwith said light tar prior to hydrocracking.

5. The process of claim 1 wherein a phenol containing stream is producedin the carbonizing step and further comprising the steps of:

extracting the phenols from said phenol containing stream; and

feeding said phenols to the hydrotreating step along with the syntheticcrude from the distilling step.

6. In a process for converting coal into synthetic petroleum crudewhich, comprises carbonizing the coal, hydrocracking liquids produced inthe carbonizlng step and separating the liquids produced in thehydrocracking step to produce said synthetic crude and naphtha, theimprovement comprising: recycling at least a portion of said naphtha forbeing mixed with the liquids produced in the carbonizing step prior tohydrocracking.

7. The process of claim 6 wherein the separating step comprises vacuumdistilling the liquids and hydrotreating at least a portion of thedistilled liquids for producing an improved synthetic crude product.

8. The process of claim 7 :wherein a phenol containing stream isproduced by the carbonizing step and further comprising the steps of:separating phenols from said stream and hydrotreating said phenols withsaid distilled liquids for including hydrotreated phenol derivativehydrocarbons in the improved synthetic crude.

References Cited UNITED STATES PATENTS 2,654,695 10/1953 Gilbert et al208-10 2,738,311 3/1956 Frese et al 20S-8 3,107,985 10/1963 Huntington208-10 2,913,397 11/1959 Murray et al 208-8 2,913,3 88 11/1959 Howell etal 208-8 3,247,092 4/ 1966 Huntington 208-10 3,018,242 l/1962 Gorin208-10 3,117,921 1/1964 Gorin 208-10 2,600,430 6/ 1952 Riblett 2018-83,442,793 5/ 1969 Carson 208-108 3,321,393 5/1967 Schuman 208-103,157,589 11/1964 Scott 20S-108 2,982,717 5/1961 Waddill 208-1083,207,688 9/ 1965 Van Driesen 208-108 DELBERT E. GANTZ, Primary ExaminerV. OKEEFE, Assistant Examiner U.S. Cl. X.R. 20S-8, 108

